The present invention relates to a data recording apparatus and, more particularly, to a data recording apparatus for a document information filing system.
A document information filing system which uses a magnetic tape or an optical disc is known as a system to replace a microfilm system. In a document information filing system of this type, a document is two-dimensionally scanned by an optical scanner. The image information for each scanning line (line image information item) from the optical scanner is compressed and is then recorded on a magnetic tape or an optical disc. Desired image information written in this manner is retrieved and is expanded for each scanning line. The expanded image information is supplied to a display device and/or electrographic printer which produces a visible image.
Errors tend to be caused in a document information filing apparatus as described above and especially in a document information filing apparatus which uses an optical disc. As a countermeasure to solve this problem of errors, error correction codes are added to the image information. In order to set an error correction code for the image information, the image information must have a fixed bit length. However, the bit length of the image information differs from one scanning line to another and varies within a range of 40 to 2,000 bit length. Thus, an error correction code cannot be set for each scanning line. For this reason, the line image information item is divided into a plurality of image data pieces of a fixed bit length. Then, an error correction code is set for each image data piece. However, with this method, the image data piece corresponding to the terminal end of each scanning line rarely has the fixed bit length. As a result of this, the image data piece at the end of a scanning line frequently contains the image data of the next scanning line. The error correction code is then set for the image data piece including image data from two scanning lines. This results in errors in error correction.